Introduction to Exception Handling in Python Exception handling in Python is a crucial mechanism that helps in managing runtime errors efficiently. Instead of crashing the program when an error occurs, Python allows developers to handle these errors gracefully using try-except blocks. This approach ensures that programs continue executing without unexpected interruptions. Why is Exception Handling Important? Exception handling is essential for: Preventing program crashes – Ensures smooth execution despite errors. Improving user experience – Provides meaningful error messages instead of abrupt termination. Maintaining data integrity – Prevents data corruption by handling exceptions properly. Debugging and logging – Helps in tracking errors systematically. Types of Errors in Python Before diving into exception handling, let’s understand the common types of errors in Python: 1. Syntax Errors – Occur due to incorrect Python syntax.pythonCopyEdit print("Hello World" # Missing closing parenthesis Output! 2. Logical Errors – Do not crash the program but produce incorrect results. 3. Runtime Errors (Exceptions) – Happen during execution and require handling. Handling Exceptions Using try-except The try-except block helps catch and handle exceptions gracefully. Basic Example try: num = int(input("Enter a number: ")) print(10 / num) except ZeroDivisionError: print("Error: Cannot divide by zero.") except ValueError: print("Error: Invalid input. Please enter a number.") Output! Explanation: The try block contains the code that may raise an exception. The except block catches specific exceptions and executes appropriate error-handling code. Handling Multiple Exceptions Python allows handling multiple exceptions within a single try-except block. try: num = int(input("Enter a number: ")) print(10 / num) except (ZeroDivisionError, ValueError) as e: print(f"An error occurred: {e}") Output! When to Use Multiple Except Blocks? When different errors need different handling approaches. When specific error messages or corrective actions are required. Using else and finally in Exception Handling Python provides additional clauses like else and finally in try-except blocks. Example: Using else and finally try: num = int(input("Enter a number: ")) result = 10 / num except ZeroDivisionError: print("Error: Cannot divide by zero.") else: print(f"Result: {result}") finally: print("Execution complete.") Output! Explanation: The else block executes when no exceptions occur. The finally block always runs, regardless of whether an exception was raised. Raising Custom Exceptions Python allows developers to raise their own exceptions using the raise keyword. def check_age(age): if age < 18: raise ValueError("Age must be 18 or above.") print("Access granted.") try: check_age(16) except ValueError as e: print(e) Output! Use Cases of Custom Exceptions: Validating user input Handling business logic-related errors Common Exceptions in Python Python has many built-in exceptions, each representing a specific error condition. Some of the most common ones include: Exception NameDescriptionBaseExceptionThe base class for all built-in exceptions.ExceptionThe base class for all non-exit exceptions.ArithmeticErrorBase class for all errors related to arithmetic operations.ZeroDivisionErrorRaised when a division or modulo operation is performed with zero as the divisor.OverflowErrorRaised when a numerical operation exceeds the maximum limit of a data type.FloatingPointErrorRaised when a floating-point operation fails.AssertionErrorRaised when an assert statement fails.AttributeErrorRaised when an attribute reference or assignment fails.IndexErrorRaised when a sequence subscript is out of range.KeyErrorRaised when a dictionary key is not found.MemoryErrorRaised when an operation runs out of memory.NameErrorRaised when a local or global name is not found.OSErrorRaised when a system-related operation (like file I/O) fails.TypeErrorRaised when an operation or function is applied to an object of inappropriate type.ValueErrorRaised when a function receives an argument of the right type but an inappropriate value.ImportErrorRaised when an import statement has issues.ModuleNotFoundErrorRaised when a module cannot be found. Additional Topics: Enums Dynamic Typing Interview Questions: 1. What is the difference between syntax errors and exceptions?(TCS) Exceptions are runtime errors that occur during execution, but they can be handled using try-except. Syntax errors occur when the code violates Python’s syntax rules, and they prevent execution. 2. Explain the difference between try-except and try-finally.(Infosys) The try-finally block ensures that the finally section executes regardless of whether an exception occurs. The try-except block catches and handles specific exceptions, preventing the program from crashing. 3. How would you implement custom exception handling in a Python-based web application?(Amazon) Implement try-except in critical sections of the application to catch and handle the exception. Create a custom exception class by inheriting from Exception. Use raise to trigger the exception when necessary.
